Molecules and
Compounds
(Nomenclature)
Chapter 5
Tro, 2nd ed.
Molecules and Compounds
Pair up and look up this law and then write it
in your own words to share with the rest of
the class. Give examples other than what
is in the textbook.
Law of Constant Composition
HOW TO LEARN
NOMENCLATURE
Memorize, memorize, memorize!
Memorize the rules for naming
Memorize names of ions
Memorize some acid names and some
organic names
Types of Compounds and Naming
Rules
Compound
Ionic (formula unit)
Salts
Hydrates
Other
Covalent (molecule)
Binary (Ternary) Organic
Acids
Other
Binary
Polyatomic Ions
You will learn all the rules for ionic, hydrates,
covalent binary, and only specific common names,
organic compounds and acids.
Common and Systematic Names
Chemical nomenclature is the system of names that
chemists use to identify compounds. Two classes of
names exist: common names and systematic names.
Common names are arbitrary names.
They are not based on the composition of the compound.
They are based on an outstanding chemical or physical
property.
Common names that you need to memorize: acetylene,
ammonia, water, baking soda, cane sugar, epsom salts,
grain alcohol, laughing gas, lye, muriatic acid, table salt,
vinegar, washing soda, and wood alcohol. (common
name, formula and systematic name)
Ammonia,
NH3
Chemists prefer systematic names.
Systematic names precisely identify the
chemical composition of the
compound.
The present system of inorganic
chemical nomenclature was devised
by the International Union of Pure and
Applied Chemistry (IUPAC).
The formula for most elements
is the symbol of the element.
Sodium
Potassium
Zinc
Argon
Mercury
Lead
Calcium
Na
K
Zn
Ar
Hg
Pb
Ca
These 7 elements are found
in nature as diatomic molecules.
Hydrogen
Nitrogen
Oxygen
Fluorine
Chlorine
Bromine
Iodine
H2
N2
O2
F2
Cl2
Br2
I2
A
charged
particle
known
as
an
ion
can
If one or more electrons are removed from a
be
produced
by
adding
or
removing
neutral atom a positive ion is formed. A
one
or
more
electrons
from
a
neutral
positive ion is called a cation.
atom.
remove e-
→
neutral atom
cation
MONATOMIC IONS:
Metals always lose electrons to form positive ions,
called cations
If element forms only one cation, we name it by its
element name:
Na+ = sodium ion
Al3+ = aluminum ion
If a transition metal can form more than one cation,
add ion’s charge in Roman numerals to the
name.
Fe2+ is iron(II) ion and Fe3+ is iron(III) ion.
(Old names, ferrous and ferric.)
If Aone
or
more
electrons
are
added
to
a
charged particle known as an ion can
neutral
atom aby
negative
ionremoving
is formed.
be produced
adding or
oneA
negative
is called
an anion.
or moreion
electrons
from
a neutral atom.
add e-
neutral atom
→
anion
MONATOMIC IONS:
Nonmetal atoms gain electrons to form negative
ions, called anions
Take the root of the element name and add “-ide”
Cl- = chloride ion
Se2- = selenide ion
N3- = nitride ion
Most often ions are formed when metals combine
with nonmetals. (Exception is NH4+ with anion.)
The charge on an ion can be predicted from its
position in the periodic table.
elements
elements of
elements
elements
of of of
elements of Group
VIA have
a
Group IIA have Group
a Group
VAGroup
have
VIIA
a have
a
IA have a +1 charge
-2 charge
+2 charge
-3 charge
-1 charge
NAMING IONIC COMPOUNDS:
Always put cation before anion in formula. Name of compound is just
cation name followed by anion name.
MgF2 is Mg2+ and F- = magnesium fluoride
FeBr3 is Fe3+ and Br- = iron(III) bromide
What is the formula for silver carbonate?
Silver ion is Ag+ and carbonate CO32- have to balance charges, so need 2 Ag+ for each CO32- = Ag2CO3
Generic: Ma+bNb-a criss-cross rule
However, if a = b, then both = 1 by definition for lowest ratio
Figure out the charge on each x:
ZnX, NH4X, (NH4)2X, Al2X3, X2(SO3)3
Write the formula of barium phosphide.
Step 1. Write down the formulas of the ions.
Ba2+ P3Step 2. Combine the smallest numbers of Ba2+
3- so that the sum of the charges
and
P
The cation
The anion
is
is
equals
zero.
written
written
first. second.
3(Ba2+) + 2(P3-) = 0
3(2+) + 2(3-) = 0 The lowest
common multiple
The correct formula is Ba3P2
of +2 and –3 is 6
Naming Compounds Containing
Polyatomic Ions
A polyatomic ion is an ion that
contains two or more
elements.
Compounds containing
polyatomic ions are composed
of three or more elements.
They usually consist of one or
more cations combined with a
negative polyatomic ion.
When naming a compound
containing a polyatomic ion,
name the cation first and then
name the anion.
NO-3
Na 2CO3
This is the way the
formula is written.
Na 2CO3
2Na
+
CO
The ions are what is
actually present.
23
Elements that Form More than One
Polyatomic Ion with Oxygen
Anions ending in -ate always contain
more oxygen than ions ending in ite.
nitrite
nitrate
2
3
phosphite
phosphate
333
4
NO
NO
PO
PO
One group of ionic compounds that contains all nonmetals is the ammonium salts.
Try to write formulas for ammonium sulfate and ammonium phosphate.
ANIONS WITH HYDROGEN
Some anions have picked up one or two
hydrogen ions. Old naming rules put “bi”
in front of the anion name. IUPAC uses
hydrogen or dihydrogen:
CO32- with one H+ added is HCO3Carbonate ion becomes hydrogen carbonate
ion.
Name these: PO43-, HPO42-, H2PO4-
Four polyatomic ions that do not use
the –ate/ite system.
hydroxide
-
cyanide
hydrogen sulfide
-
peroxide
22
OH
HS
CN
O
-
There are three common positively
charged polyatomic ions.
mercury(I)
2+
2
Hg
hydronium
+
3
HO
ammonium
+
4
NH
Divide the formula into cation(s) and anion. Name each.
For example KHSO4 is K+ and HSO4-.
MgNH4PO4 is Mg2+, NH4+ and PO43-.
(So you can see relationship between anions and acids.)
Binary Compounds
Binary compounds contain only two different elements. There
are four main types, listed in following slides.
Binary Ionic Compounds Containing a Metal Forming
Only One Type of Cation (salts)
Binary ionic compounds consist of a metal combined with a nonmetal.
The chemical name is composed of the name of the metal
followed by the name of the nonmetal which has been
modified to an identifying stem plus the suffix –ide.
Using this system the number of atoms of each element present is
not expressed in the name.
Practice: CaC2, MgBr2, Al2O3, NaH
(calcium carbide, magnesium bromide, aluminum oxide, sodium
hydride)
A.
Binary Compounds
B. Binary Ionic Compounds Containing a Metal
That Can Form Two or More Types of Cations (still salts)
The chemical name is composed of the name of the metal with its
charge in Roman numerals, followed by the name of the
nonmetal which has been modified to an identifying stem plus
the suffix –ide.
Using this system the number of atoms of each element present is
not expressed in the name.
Practice: FeS, CuCl2, SnF2, Mn3(PO4)5
(iron (II) sulfide, tin(II) fluoride, manganese (V) phosphate)
Ion Names: Classical System
Lower Charge
Higher Charge
Element
Formula
Name
Formula
Name
Copper
Cu+
cuprous
Cu2+
Cupric
Iron
Fe2+
ferrous
Fe3+
ferric
Lead
Pb2+
plumbous
Pb4+
plumbic
Mercury
Hg2+
mercurous Hg2+
Tin
2
Sn2+
stannous
Sn4+
mercuric
stannic
This is for information and for homework only; classical names will not be on quiz
or test unless part of a common name that’s required.
Binary Compounds
C. Binary Compounds Containing Two Nonmetals (Binary
Covalent) Compounds between nonmetals are
molecular, not ionic.
In a compound formed between two nonmetals, the
element that more electropositive (least electronegative)
is named first.
Rules for naming:
1. Give Greek prefix (to indicate number of atoms of first
element) to name of first element. Don’t use mono prefix
for first element.
2. Give Greek prefix (to indicate number of atoms of
second element) to root of element name, then add -ide
Example: N2O3 is dinitrogen trioxide.
Exception: hydrogen never has prefix.
Greek Prefixes
mono = 1
di = 2
tri = 3
tetra = 4
penta = 5 hexa = 6
hepta = 7 octa = 8
nona = 9
deca = 10
Binary Compounds
C. Binary Compounds Containing Two Nonmetals (Binary Covalent) Examples
N2O3, PCl5, Cl2O7, CCl4, CO, CO2, PI3, H2S
Dinitrogen trioxide
Phosphorous pentachloride (not mono-)
Dichlorine heptoxide
Carbon tetrachloride
Carbon monoxide
Carbon dioxide
Phosphorous triiodide
Hydrogen sulfide (hydrogen never gets a prefix)
Now try: CS2, H2O, N2O4, SF2, SiCl2, P2O5, phosphorous trichloride,
dichlorine oxide
Binary Compounds
D. Acids Derived from Binary Compounds
Certain binary hydrogen compounds, when
dissolved in water, form solutions that have acid
properties.
The aqueous solutions of these compounds are
given acid names.
The acids names are in addition to their –ide
names.
Hydrogen is typically the first element of a binary
acid formula.
Acid Formation
binary hydrogen
compound like
HCl is called
hydrogen
chloride (not an
acid yet).
water
Acid sol.
Now it’s hydrochloric acid.
Binary Compounds
D. Acids Derived from Binary Compounds
To name binary acids write the symbol of hydrogen
first. After hydrogen write the symbol of the
second element.
Place the prefix hydro- in front of the stem of the
nonmetal name. Place the suffix -ic after the
stem of the nonmetal name.
Practice: HCl, H2S, HI
(hydrochloric acid, hydrosulfuric acid, hydroiodic
acid)
D.
A.
C.
B.
More Acids
Oxy-acids contain
hydrogen, oxygen
and one other
element.
Hydrogen in an
oxy-acid is not
expressed in the acid
name.
The other element is
usually a nonmetal, but it
can be a metal.
The first element listed in
the formula is hydrogen.
The remaining
elements include oxygen
and form a polyatomic
ion.
The word acid in the name
indicates the presence of
hydrogen.
indicates
hydrogen
sulfuric acid
contains
contains
contains
hydrogen
sulfur
oxygen
H 2SO 4
This is one of the six acids you have to know.
(If you add HCl to the ones marked by arrows, you have your total list of acids.)
Your Acids
An acid is a substance that forms H+ when
dissolved in water
Some are strong acids, that means all the H+
dissolves and dissociates from the anion
Some acids are weak, meaning very little H+
dissociates, although the cmpd dissolves
Forget sections in text: just learn these!
Hydrochloric acid, sulfuric acid, and nitric acid
are strong acids: HCl(aq), H2SO4(aq), HNO3(aq)
Acetic acid, carbonic acid, phosphoric acid are
weak acids: HC2H3O2(aq), H2CO3(aq), H3PO4(aq)
Your Organic Compounds
No naming rules – just learn formulas and
names.
CH4 methane, C3H8 propane, C8H18 octane,
CH3OH methanol, CH3CH2OH ethanol,
C6H6 benzene, CH3COOH acetic acid
(organic method), CH3NH2 aminomethane,
C6H12O6 glucose, C12H22O11 sucrose, and
C2H2, ethyne
HYDRATES: (not in book)
Also a good review of ionic names!
If an ionic compound is a hydrate, it will
have *H2O in the formula, like MgCO3*6
H2O
Name the ionic compound part using ionic
naming rules, then give the Greek prefix
for the number of water molecules and
add the word hydrate:
MgCO3*6H2O is magnesium carbonate
hexahydrate
HYDRATES: (not in book)
Also a good review of ionic names!
Examples: you name the following (notice their
common names)
gypsum
CaSO4*2 H2O
epsom salts MgSO4*7 H2O
washing soda Na2CO3*10 H2O
bluestone
CuSO4*5 H2O
Calcium sulfate dihydrate
Magnesium sulfate heptahydrate
Sodium carbonate decahydrate
Copper(II) sulfate pentahydrate
Formula Mass
As each element’s atom has mass in amu
on the Periodic Table, so do molecules
and formula units.
Formula mass is the sum of the atomic
masses of the atoms in the chemical
formula.
Practice: water, sodium chloride, acetic acid